14,261 research outputs found
Microdosimetric concepts relevant to HZE-particles
The biological effectiveness of HZE-particles
i s determined by the extreme microscopic concentrations
of energy transfer in the vicinity
of the particle tracks. The concept of linear
energy transfer fails to describe this situation
adequately. The more rigorous microdosimetric
concepts are presented. A simplified
treatment, based on the radial distribution
of energy around the track core, is then considered
Testing and evaluation of solid lubricants for gas bearings
The testing and results of testing solid film lubricants for gas lubricated bearing applications are reported. The tests simulated operational hazards of tilting pad gas bearings. The presence of a low coefficient of friction and the endurance of the solid film lubricant were the criteria for judging superior performance. All solid lubricants tested were applied to a plasma sprayed chrome oxide surface. Molybdenum disulfide and graphite fluoride were the solid lubricants tested; other test parameters included the method of application of the solid lubricant and the surface finish of the plasma sprayed coating. In general, the application of a solid film lubricant was found to significantly improve the coefficient of friction of the rubbing surfaces
Structure formation by cosmic strings with a cosmological constant
Final published version.Comment: 4 Page
Doppler peaks from active perturbations
We examine how the qualitative structure of the Doppler peaks in the angular
power spectrum of the cosmic microwave anisotropy depends on the fundamental
nature of the perturbations which produced them. The formalism of Hu and
Sugiyama is extended to treat models with cosmic defects. We discuss how
perturbations can be ``active'' or ``passive'' and ``incoherent'' or
``coherent'', and show how causality and scale invariance play rather different
roles in these various cases. We find that the existence of secondary Doppler
peaks and the rough placing of the primary peak unambiguously reflect these
basic properties.Comment: uufile, 8pages, 3 figures. Now available at
http://euclid.tp.ph/Papers/index.html; Changes: URL added, Eqn. (8) expanded,
grant numbers include
Survival curves and age response functions for chinese hamster cells exposed to X-rays or high LET alpha-particles
A Closed-Form Expression for the Gravitational Radiation Rate from Cosmic Strings
We present a new formula for the rate at which cosmic strings lose energy
into gravitational radiation, valid for all piecewise-linear cosmic string
loops. At any time, such a loop is composed of straight segments, each of
which has constant velocity. Any cosmic string loop can be arbitrarily-well
approximated by a piecewise-linear loop with sufficiently large. The
formula is a sum of polynomial and log terms, and is exact when the
effects of gravitational back-reaction are neglected. For a given loop, the
large number of terms makes evaluation ``by hand" impractical, but a computer
or symbolic manipulator yields accurate results. The formula is more accurate
and convenient than previous methods for finding the gravitational radiation
rate, which require numerical evaluation of a four-dimensional integral for
each term in an infinite sum. It also avoids the need to estimate the
contribution from the tail of the infinite sum. The formula has been tested
against all previously published radiation rates for different loop
configurations. In the cases where discrepancies were found, they were due to
errors in the published work. We have isolated and corrected both the analytic
and numerical errors in these cases. To assist future work in this area, a
small catalog of results for some simple loop shapes is provided.Comment: 29 pages TeX, 16 figures and computer C-code available via anonymous
ftp from directory pub/pcasper at alpha1.csd.uwm.edu, WISC-MILW-94-TH-10,
(section 7 has been expanded, two figures added, and minor grammatical
changes made.
Following a "Collapsing" Wavefunction
I study the quantum mechanics of a spin interacting with an ``apparatus''.
Although the evolution of the whole system is unitary, the spin evolution is
not. The system is chosen so that the spin exhibits loss of quantum coherence,
or ``wavefunction collapse'', of the sort usually associated with a quantum
measurement. The system is analyzed from the point of view of the spin density
matrix (or ``Schmidt paths''), and also using the consistent histories
approach. These two points of view are contrasted with each other. Connections
between the results and the form of the Hamiltonian are discussed in detail.Comment: 30 pages, plain LaTex, 3 figures in a separate uuencoded fil
FOZO, HIMU, and the rest of the mantle zoo
Author Posting. © American Geophysical Union, 2005. This article is posted here by permission of
American Geophysical Union for personal use, not for redistribution. The definitive version was published
in Geochemistry Geophysics Geosystems 6 (2005): Q05007, doi:10.1029/2004GC000824.The parameter μ describes the 238U/204Pb ratio of an Earth reservoir. Mantle domains labeled HIMU (high μ) originally defined reservoirs with highly radiogenic Pb isotope ratios observed in basalts from a select number of ocean islands, St. Helena in the Atlantic Ocean and the Cook-Austral islands in the South Pacific Ocean. While some authors use the term HIMU in this original sense, others refer to HIMU as a widespread component in many mid-ocean ridge and ocean island basalt (MORB and OIB) sources. Here we show that highly radiogenic Pb isotope signatures in MORB and OIB originate from two different sources. In addition to the classical HIMU component observed at St. Helena and the South Pacific (named HIMU in the following), we define a component with slightly less radiogenic Pb but significantly more radiogenic Sr isotope signatures. This component lies at the extension of the (Atlantic and Pacific) MORB array in a Sr-Pb isotope ratio diagram and is argued to be a ubiquitous component in MORB and many OIB sources. The inferred role of this component in the mantle and its inferred genetic origin closely resemble those originally suggested for a mantle component termed FOZO by Hart and coworkers. By redefining the composition, the origin, and the role of FOZO in the mantle, we establish a simple conceptual framework that explains the isotopic variability in both MORB and OIB with the lowest number of components. OIB are grouped into HIMU-type OIB and basalts from islands that diverge from the MORB-FOZO array toward various isotopically “enriched” compositions (EM). The apparent ubiquity of FOZO in the mantle and the calculated isotopic evolution of compositionally diverse MORB suggest that normal mantle melting and continuous subduction and aging of that crust during recycling through the mantle are the dominant causes of the MORB-FOZO array. In contrast to FOZO, HIMU-type OIB are quite rare, and if an origin by recycling of oceanic crust is also postulated, the production of HIMU sources has to be a special and rare combination of age and composition of subduction-modified recycled oceanic crust.This work is partially supported by the Deutsche Forschungsgmeinschaft (DFG grant STR853/1 to A.S)
A Comparison of the Ovulation Method With the CUE Ovulation Predictor in Determining the Fertile Period
The purpose of this study was to compare the CUE Ovulation Predictor with the ovulation method in determining the fertile period. Eleven regularly ovulating women measured their salivary and vaginal electrical resistance (ER) with the CUE, observed their cervical-vaginal mucus, and measured their urine for a luteinizing hormone (LH) surge on a daily basis. Data from 21 menstrual cycles showed no statistical difference (T= 0.33, p= 0.63) between the CUE fertile period, which ranged from 5 to 10 days (mean = 6.7 days, SD = 1.6), and the fertile period of the ovulation method, which ranged from 4 to 9 days (mean = 6.5 days, SD = 2.0). The CUE has potential as an adjunctive device in the learning and use of natural family planning methods
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